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Old 8th February 2013, 10:53 AM   #181
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Quote:
Originally Posted by johnthesoftware View Post
Well, I didn't expect it to sound better than the JLH, just LOUDER, which it is, but the bass is ill-defined. There's a lot more of it at the lower end, which is fine, but it seems to swallow up all adjacent frequencies so, for instance, the ridiculously over-recorded double bass on the more recent Jacques Loussier records which sounds so fantastic on my JLH just sounds wooly on the PLH. Similarly Eminem (excellent recordings, who'd have thought).
I beleive your point is correct, since I also assembled and listened to several similar amps, that differ mainly by a kind of output transistors.
Not speaking about overall sound, but only about naturality of bass, I could state, that bass gets better in this order
LMOSFET-VMOSFET-Si BJT-Ge BJT
Output impedance modulus does not say much about bass naturality.
For instance, 1mOhms Rout with lateral MOSFETS, achieved due to deep GNFB, produce nevertheless much more "gentle" and "plain" bass, than 100mOhms Rout with BJTs at No GNFB schematics.
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Old 8th February 2013, 11:03 AM   #182
flg is offline flg  United States
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I'm not sure I undestand the cap thing. By making these series caps smaller you are high pass filtering. Cuttin off the bass! You might want to try more cap
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Old 8th February 2013, 11:32 AM   #183
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Originally Posted by flg View Post
I'm not sure I undestand the cap thing. By making these series caps smaller you are high pass filtering. Cuttin off the bass! You might want to try more cap
I guess he meant the replacement 1x10000 by 10x1000
From my listenings, 10000 is not enough anyway (in spite that passband seems OK).
I would recommend, just try, adding 2x10000 more (possibly via 0,03...0,05 Ohms resistor, if these additional caps are lesser in quality than the first caps)
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Old 8th February 2013, 04:18 PM   #184
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No, I did reduce the capacitance thereby high-pass filtering. It was my opinion that there was too much bass, so it was deliberate, and it increased the definition. It's as if there's a general resonance at lower frequencies.

Anyway, the point has become moot. The wind must have changed, I turned my back on them for half an hour and one of them fried.

I have become disillusioned and am going to the pub to talk about anything other than diy audio.
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Old 9th February 2013, 05:37 AM   #185
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Could the problem with too much bass be the low damping factor of the PLH?
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Old 9th February 2013, 08:11 AM   #186
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Ah ha, I think you're probably right Loudthud, I didn't think of that (this is mostly a learning exercise). A quick sim on both circuits shows the output impedance of the PLH to be about 2 and the JLH 0.16, a big difference.

Sadly there's not enough gain in the PLH to allow me increase the feedback. I would pursue this, but the fact that the quiescent current increases with temperature means either much bigger heat sinks or some sort of current control circuitry (much cheaper than the heatsinks), but it means repackaging the whole thing.

I'm going to consign this one to history and use my stock of FETs to drive my anti-gravity device.

Thanks to all for your help.

John
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Old 9th February 2013, 04:33 PM   #187
knutn is offline knutn  Norway
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I have made a JLH/PLH amplifier, see NOStalgia - the all-FET JLH/PLH Class A amplifier. The additional gain in the input stage is sufficient to lower the output impedance.
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Old 9th February 2013, 07:00 PM   #188
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Quote:
Originally Posted by knutn View Post
I have made a JLH/PLH amplifier, see NOStalgia - the all-FET JLH/PLH Class A amplifier. The additional gain in the input stage is sufficient to lower the output impedance.
I like the way the DC drop across R14 in the Nostalia is swollowed up by the Gate-Source voltage of the JFET. Any update on the performance of that amplifier in areas on DC offset-drift, distortion numbers and output impedance?
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Old 10th February 2013, 09:45 AM   #189
knutn is offline knutn  Norway
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The DC offset was trimmed to be zero, and the variation afterwards was very small, less than 50 millivolts, if I remember right. The distortion was measured at 1 kHz with a 32 volt peak to peak output signal into eight ohms to be about -67 dB both second harmonic (2H) and third harmonic (3H) for the amplifier with the push pull output configuration. With single ended output was 2H: -49 dB, 3H: -58 dB, 4H: -70 dB and 5H: -79 dB. The distortion increased a little with an increase in the frequency. The idle current was set to 1.6 Ampere. With 2 Ampere, the distortion was lower. By now I am running the amplifier in push-pull mode with 1.6 Amperes idle current. The output impedance is measured to be about 0.4 ohms with this configuration. I am very pleased with this amplifier, but I think I would recommend a capacitance multiplier power supply, at least for the negative leg.
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Old 21st April 2013, 12:04 PM   #190
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Q1 from the PLH amplifier schematic does need a heat sink? How much power will dissipate?
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